>Toastmasters recommends that to be heard well speaking into a large area>one should raise the pitch of his voice. Politicians do it all this>time. Now, I don't know about the physics, but I believe my own ears. >Higher pitches are better for hearing.

This corresponds to a story that a woman told me about her mother during World
War II. It seems that her mother's contribution to the war effort was to
record messages to be played to pilots flying airplanes. The scientists found
that a high pitched female voice giving orders to the pilots while busily
engaged got their attention better than did a low pitched male voice. The
situation that you are describing may actually relate to human attention.

An alternative is that in a large filled room, there is a background droning
hum of low-pitched sound due to those sounds carrying farther - to avoid being
cancelled out by background noise one must speak loudly with a different or
higher pitch. I own a white noise generator machine which can be tuned to
different frequencies depending on the frequency of the sound that one is
trying not to hear. To not hear low-pitched music, you set it for a
waterfall noise at a constant somewhat low-pitched frequency, or similarly
raise the frequency to not hear high-pitched noise.